The present invention relates, in general, to an electric machine, and to a method of making such an electric machine.
External rotor motors are generally known to have an external rotor which is rotatable about a rotation axis. Disposed in coaxial relationship to the rotation axis inside the external rotor is a stator having slots for receiving the stator winding, whereby the slots taper in a direction to the rotation axis. The stator is formed about its outer circumference with small openings in the slots for wrapping the winding to the stator. In the event, it is desired to fill the slot with winding as much as possible, the winding operation become cumbersome because the stator winding must be wound through the narrow openings.
The coils of the stator winding may hereby be mounted by means of needle winding technique, flyer technique, draw-in technique, or manual guiding-in technique, into the slots. Using a needle arrangement to wind a copper coil results only in a limited slot filling degree so that the power density in the motor is decreased. The draw-in technique requires a prolongation of the winding end portion so that the coil exhibits a higher electrical resistance, accompanied by greater losses in the motor. The manual guiding-in technique is labor-intensive and thus expensive.
In particular when exciter coil windings are involved, the broad tooth tips of the slots require a flexible copper coil. Thus, the winding quality becomes substandard, when the winding operation is carried out automatically.
It would therefore be desirable and advantageous to provide an improved electric machine and method of making an electric machine to obviate prior art shortcomings.